993GT

I'm thinking its not a starvation issue per se, but rather the pump isn't able to meet the duty-cycle you're asking from it, ie 600hp + 30C(?) ambient + hot engine bay temps, etc ... the fuel and pump are getting too hot to keep up, might be why the 997 went to dual in-tank pumps(which is my plan when I replace my pump).
Definitely worth a log under these conditions too.
Cheers,

powdrhound

I don't think I'm anywhere near 600hp and with the larger injectors wouldn't think duty cycle would be an issue. However, if the pump is marginal, maybe that is the case when combined with high lateral G's. I still don't see how that would correlate to the 3/4 and full throttle issue I mentioned earlier. I just ran yesterday at the track when it was very cool with ambient temps around 10C and it was doing it just the same as on a 30C day. Something strange is afoot... lol.

Regarding the dual 997Tt pump set up, I spoke to Kevin about it and my understanding is that it's not really an option without rather extensive machining and modifications to make it work. I assume if it was doable, you'd already see it being done or some vendor would have put a kit together already. Kevin did mention running the battery directly to the fuel pump to minimize losses so that the pump would be getting the most juice. Or something along those lines... I've never been good when it comes to wiring, I drive an ice cream truck for a living...

993GT

well let's say at least mid 500's hp, crank, or ~500whp.
The injectors don't help with the pump duty cycle, injector duty cycle yes but not the fuel pump itself.
I agree, different issue from the 3/4 throttle issue, I think.
Definitely some strange going on, but a log will be a great starting point.
Seems to be some guys on 6S.O. with the 997 upgrade, but am continually researching it...definitely possible with some small tweaks.
Would be a sweet upgrade to do the 90L 997 tank with pump...
Trying a big direct power line to the pump w. HD relay would be worth a shot, can only help

powdrhound

The only thing I see us that the fuel pump might be a bit marginal and not supply enough fuel when subjected to lateral Gs. This is impossible to log on the street because there are no places to pull 1+G turns on the street. It's also hard to do on the track because you can't lug a laptop with you. Does anyone make a larger capacity fuel pump that would be a direct replacement for the stock one?

993GT

Definitely not a street test, would have to be a track test, maybe Velcro the laptop down or have a co-driver cycle it when on a open lapping day, need to replicate the scenario.
Don't know of any factory-like plug-n-play upgrades, short of the 997 idea.

wross996tt

I agree with the fuel theory. Are you running the stock FPR? I use the 5bar FPR with Kevin's setup. Others go different routes to increase the fuel flow (rails, two pumps, etc.). It seems like 1.3 is high for your set-up?, but what the heck do I know...LOL

powdrhound

My set up is Kevin's zero clearance turbos with his injectors and his custom programming. Kevin did not want to do a 5 bar fpr for my application but opted for injectors with a 3.8 fpr to provide better fueling margins since my car is pretty much 100% track The bogging I sometimes experience in a high G (generally greater than 1.2G) right handed turn even happens at part throttle during acceleration. One thing that has crossed my mind is that maybe the ECU is seeing the high speeds of 90+mph coupled with high G loadings and is retarding the throttle. I'm not sure if that's possible as there is no PSM on this car, only ABS just like on a GT2.

I don't think 1.3bar is too high. It's actually the same as I had with my RUF turbos and RUF ECU. At least on the in dash gauge it indicated 1.3 on both set ups.

noble1978

engine tdc, intake manifold hose off and 20psi.

noble1978

where are the check valves??

noble1978

Powder hound. My throttle opening and demand are the same as yours. It's strange eh? I thought it was a problem as its a new throttle body but I've been assured it's not.

"02996ttx50

^ i think that pwdrhounds car may have reached the limit of its ability to deliver the fuel at hi demand moments. but i always assumed with his setup he'd be running the dual bosch setup. thats might well solve the issue. but i am admittedly out of my depth. rob's kicking ***. good advice

noble1978

So where are all these nrv s I need to be checking. Are they all accessible without too much work or is it a garage job??

"02996ttx50

there's two. one above the plenum, and the other below that ( forgive me ) looks like a very small round piece of fishing tackle! ( serious )

they are SO cheap that replacing them ALL at once as a preventative is very wise. the one that i discovered being cracked was the one just above the plenum.

the minute i hooked the pressure tester to the turbo to pressure test, it whistled dixie and it was indeed cracked ( they're plastic ) once i replaced all # ( incl the n75!! ) and went back to stock adjustment on my 1.0 bar waste gates my car ran better than since i first took possession of it.

leaks are that hidden and serious to the overall smooth running and optimal performance of the car. i find. the valves are cheap as hell. change them! and good luck man. its frustrating, don't i ( we all! ).. know

Tuxiemama

OP and pwderhound

datalog your cars, upload it to datazap.me and post here.... some tunes seem to have a boost to max to around 6000 rpms then boost drops off and then there is an overspike

I have seen it on my old GIAC tune, my old Eurodyne tune, my mate's Proto tune... my problem was solved by Tim who tunes my car and with a MAFLESS set up seems to disappear for everyone I talk to

but datalog it and lets look at things like IDC% etc

noble1978

Cheers for the info 996ttx50

I'll do the logs tomorrow, I'm home alone with a 2 and 5 year old!